D,L-phosphinothricin (commonly referred to as glufosinate) and its salts and esters are known to be useful as a broad spectrum, non-selective herbicide. The ammonium salt of phosphinothricin is the most common commercially available form. The herbicidal efficacy of L-phosphinothricin or salts and esters thereof is generally about twice that of other stereoisomers, thereby generally requiring a reduced proportion of herbicide to provide the desired effect. Thus, the use of the L-stereoisomer is economically and ecologically advantageous.
Various multistep processes to prepare phosphinothricin are known in the art. For example, some routes utilize phosphorus trichloride to produce a phosphinate precursor, which is subjected to hydroformylation-aminocarbonylation, followed by hydrolysis to produce phosphinothricin. In particular, one process for producing phosphinothricin generally comprises converting phosphorus trichloride to methylphosphonous dichloride or a derivative thereof. The methylphosphonous dichloride or derivative thereof is then reacted with methanol to form methyl methylphosphinate. Methyl methylphosphinate is then reacted with vinylic compounds (e.g., vinyl acetate) to form an intermediate (e.g., 2-(methoxy(methyl)phosphoryl)ethyl acetate). The resulting intermediate is pyrolyzed to prepare a vinylphosphinate precursor. The vinylphosphinate precursor is subjected to hydroformylation-aminocarbonylation, followed by hydrolysis of the hydroformylation-aminocarbonylation product in the presence of hydrochloric acid to produce phosphinothricin.
Another process of producing phosphinothricin generally comprises converting phosphorus trichloride to an adduct of methylphosphonous trichloride and aluminum tetrachloride (i.e., CH3PCl3.AlCl4). The adduct is reacted with ethylene to form an intermediate adduct, which is then reacted with ethanol to form ethyl 1-(2-chloroethyl)-methylphosphinate. This compound is reacted with potassium hydroxide and ethanol to prepare an ethyl vinylphosphinate precursor. The ethyl vinylphosphinate precursor is subjected to hydroformylation-aminocarbonylation, followed by hydrolysis of the hydroformylation-aminocarbonylation product in the presence of hydrochloric acid to produce phosphinothricin.
Other processes for producing phosphinothricin are described in, for example, U.S. Pat. Nos. 4,521,348; 6,335,186; and 6,359,162.
Although processes for the preparation of phosphinothricin are known in the art, there exists a need for a process that represents an improvement in process economics by virtue of requiring fewer process steps and fewer reagents than conventional processes. There also exists a need for an economical stereoselective process that preferentially produces L-phosphinothricin products or precursors thereof.